Clinical Laboratory Core will provide centralized, quality controlled services for specimen processing and management, clinical and virologic laboratory testing, and study-specific tests. The specific functions of the Core are: I. To process biological samples collected in the clinical studies (Project 1, 2) and from dengue vaccine study subjects (Project 3). Core Laboratory will maintain and manage the sample inventory and sample distribution among collaborating laboratories. II. To perform diagnostic serologic and virologic assays for Projects 1, 2 and 3 a. serological diagnosis of acute dengue virus infections using enzyme immunoassay (EIA) and hemagglutination inhibition assay (HAI). b. measurement of dengue serotype-specific neutralizing antibodies by plaque reduction neutralization assay. c. rapid diagnosis of acute dengue virus infections by qualitative dengue virus RT PCR assay. d. isolation of dengue viruses from plasma samples using Toxorrhynchites splendens mosquitoes. III. To quantify the viral burden. a. measurement of dengue virus RNA levels using a fluorogenic RT PCR assay in plasma/serum samples from acutely infected subjects for Projects 1, 2, and 3. b. measurement of NS1 antigen levels by serotype-specific ELISA in plasma/serum of acutely ill subjects for Project 1, 2, and 3. IV. To perform flow cytometry analyses on fresh blood samples for Projects 1 e.g. detection of activated T cells and functional characterization of dengue-specific T and B cells during an acute infection.